Formation of storage cavities in salt domes



y 1963 h. D. MYERS, JR

FORMATION OF STORAGE CAVITIFS IN SALT HOMES Filed June 9,1958

2 Shuts-Sheet 1 FIG. I.

May 7, 1963 R. D. MYERS, JR 3,088,717

' Foam-non 0F STORAGE CAVITIES IN SALT moms Filed June 9; 1958 2 Sheets- Sheet 2 N 9 LL I 3 Q 9 7 LL O 61 0 1- 2 m LL +a m:

S 2' E g 2 N5 Q5 I FRESH WATER United States .atent 3,088,717 FORMATION OF STORAGE CAVITIES IN SALT DOMES Richard D. Myers, Jr., Dallas, Tex., assignor, by mesne assignments, to Socony Mobil Oil Company, Inc, New

York, N.Y., a corporation of New York Filed June 9, 1958, Ser- No. 740,941 2 Claims. (Cl. 262-3) This invention relates to the development of a cavity in a salt formation and more particularly to the method of control-ling the shape of a salt cavity and the removal of insoluble materials to provide under-ground storage facilities.

Underground reservoirs employed for the storage of LPG products are attractive economically as they may be formed at a cost which is low compared to the cost of surface storage facilities and may be operated with low product loss. It is desirable that an underground storage reservoir be roughly conical in shape in order that it may be structurally sound. Various methods have been proposed for forming cavities so that they will have such form. In so forming the cavity, insoluble materials in the formations in which a cavity is to be formed cause substantial difliculty.

The present invention is directed towards the provision of a method for forming and for enlarging a cavity which will permit prolonged, continuous leaching or washing cycles with the end result that a cavity of desired shape will be formed with a minimum of alteration to the system in the course thereof.

More particularly in accordance with the present invention, there is provided a method of enlarging a cavity in a formation in which substantial amounts of insoluble material are embedded in a matrix of soluble material. A solvent is pumped into said cavity at an input point a first distance substantially above the bottom of the cavity and is removed from the cavity at a point in the region of the top of the cavity. Pumping is continued until the pressure required to maintain flow of the solvent into the cavity undergoes a substantial increase. A liquid is then pumped into said cavity at a point near the top thereof while removed initially from a second point a second distance above the bottom of the cavity which is greater than the firs-t distance above-mentioned. The second distance is then gradually decreased until it is substantially zero in order to entrain insoluble materials in the bottom of said cavity in said liquid for removal from said cavity. Thereafter, solvent is again pumped into said cavity at said input point for further enlarging the cavity.

In a more specific aspect of the invention, there is provided a method of enlarging a cavity in a soluble formation wherein a first flow channel extends from the eanths surface into the soluble formation to the total depth or desired bottom of the cavity. A second flow channel is provided terminating in the region of the upper end of the desired cavity. A solvent is then introduced into the cavity through the first flow channel having a washing orifice located a substantial distance above the total depth. This solvent is continued to flow until surface pressure in the first flow channel begins to increase. Thereafter, the washing orifice is raised and saturated solvent is injected into the cavity through the second flow channel and out through the washing orifice and the first flow channel while simultaneously lowering the washing orifice to the total depth of the cavity thereby to remove any insoluble materials collected in and around the bottom of the first flow channel. Said first flow channel is then elevated so that the washing orifice is at said same distance ice above total depth. The aforementioned steps are then repeated until the cavity reaches the desired volume.

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a cavity-forming system in accordance with the present invention; and

FIGS. 2-7 are a series of illustrations showing steps of progressively increasing a cavity size in accordance with the present invention.

Referring to FIG. 1, a borehole 10, drilled in the usual fashion as by the use of rotary drilling equipment (not shown), has surface casing which extends to the region of the caprock. More particularly, surface casing 11 is set and cemented to a depth somewhat above the salt formation 12. A smaller diameter hole has a second string of casing 14 cemented with the bottom thereof below the top of the salt formation. A third string of casing 15 of still smaller diameter is cemented with the bottom at a depth substantially below the top of the salt formation 12. The borehole it is completed through the casing 15 to the total depth 16. The initial outline of borehole 10 is shown in FIG. 1, partially in dotted lines, below the bottom of the casing 15.

When the borehole 10 has been drilled to the total depth 1-6, a temporary string of casing 18 is suspended in the borehole from a washing tree 20 which is mounted over the well at the earths surface, secured to and supported by the casings 11, 14 and 15. The temporary casing 18 is adapted to provide a fluid flow path into the well which is connected to lines 21 and 22 of the washing tree 20.

A string of tubing 23 is also hung in the washing tree and is coupled to a flow channel 24. A line 25 is connected to a source of fresh water and is connected by way of channel 26 and valve 27 to channel 22. Line 25 is also connected by way of channel 28 and valve 29 to channel 24. Channel 24 additionally is connected by way of valve 30 to a line 31 which leads to a suitable settling pit. Channel 21 is connected by way of valve 32 to line 31 which leads to the settling pit.

Preliminary washing or cavity-forming operations are then initiated. Fresh water flowing from channel 25, 28, valve 29 and channel 24 passes down tubing 23 and out of the tubing at or near the bottom thereof through a washing orifice 23a. The salt is then taken into solution and carried upward and out of the hole through the annulus between tubing 23 and the temporary casing 18 and thence through channel 21, valve 32 to flow line 3-1 leading to a settling pit. Such preliminary operations preferably are followed until an initial cavity is formed which is substantially less than the total desired capacity. The preliminary operation preferably is carried out with the washing orifice of tubing 23 at or near the bottom of the hole 10 as illustrated in FIG. 2.

The fresh water contact with the salt at the bottom of the hole produces leaching action at the highest rate at the bot-tom, which rate diminishes as the solvent becomes more saturated in its travel uphole.

As the salt is leached from the formation, insoluble materials fall to the bottom of the hole. This action, if continued for extended periods, ordinarily will prevent further introduction of fluids through pipe 23 because of sloughing action of insoluble materials. When this happens, the tubing 23 may be pulled and the insoluble materials washed from the cavity before further leaching operations are undertaken. Since repeated cleaning operations involve substantial expenditures and incur substantial delays in the leaching operations, it has been prise as much as 8% to 10% of the total solids encoun tered.

More particularly in accordance with the present invention, applicant has found that after borehole 10, FIG. 2, has been enlarged to form an initial cavity 50,.such as shown in FIG. 3, it may then be enlarged to the desired final capacity by operations altered to conform with the following program.

The depth of discharge of fresh water through the Washing orifice 23a of tubing 23 into the initial cavity 50, FIG. 3, is elevated a substantial predetermined distance above the bottom of the cavity. More particularly, the bottom of tubing 23 is raised above the cavity bottom 16 a distance which has been found to be preferably of the orderof 30 to 60 feet. Thereafter, fresh water is circulated into the cavity through the tubing 23 and out through the annulus between tubing 23 and the casing 18. As the fresh water travels upwardly through the cavity, it becomes more nearly saturated so that the brine at the top of the cavity is much less effective than at the bottom of the cavity. The result is the formation of a relatively symmetrical conical-shaped cavity.

Insoluble materials which are not carried out through the temporary casing 18 with the leaching solvent fall to the bottom of the cavity and ultimately reach a level which is above the washing orifice 2311 at the bottom of the tubing 23. Such condition is illustrated in FIG. 4 where an insoluble material fills the bottom of the now enlarged cavity 50. The existence of this condition is evidenced first by a rise in the pressure measured on the tubing at the earths surface as by means of a gauge 40. As the insoluble material piles up around the lower end of tubing 23, the pressure on tubing 23 will continue to increase. Ultimately, the tubing 23 will become plugged and leaching operation must then be stopped.

Cleaning operation comprises raising the tubing to a point above the top of the insoluble material in the cavity 50, as shown in FIG. 5, preparatory to initiating circulation in direction the reverse of that employed during leaching operation. Preferably saturated salt solution or brine is circulated down into cavity 50 through the annulus between the tubing 23 and the casing 18 and out through the tubing 23. The effluent from tubing 23 is then carried to a suitable settling pit. During the reverse circulation cycle the tubing 23 is slowly lowered into the insoluble material in the bottom of cavity 50. Reverse circulation and lowering of the tubing 23 are continued until the Washing orifice is substantially bottomed in the cavity and until no further insoluble material falls out of the solution as it is emptied into a settlingpit, a condition illustrated in FIG. 6 in idealized form. Only debris having dimensions no greater than that which will pass through pipe 23 will be removed, and such debris is referred to in this application as insoluble debris.

Normal circulation is then re-established and leaching operations undertaken by injecting fresh water through tubing 23. As in the operations illustrated in FIG. 3, the bottom of the washing orifice of tubing 23 is again raised to a point well above the bottom of the cavity 50, as shown in FIG. 7, so that the leaching operations may be continued for a substantial period before the insoluble material causes the pressure to rise on tubing 23.

In carrying out the method of the present invention in one instance, the top of the salt was encountered at about 700 feet below the surface and the hole was initially drilled to a total depth of 2400 feet. Casing was provided as illustrated in FIG. 1, the casing 11 of diameter 4 being set to a depth of about 300 feet. The casing 14 of 13%" diameter was set to a depth of about 800 feet. Casing 15 of 10%" was set to a depth of about 1100 feet. The temporary casing 18 was 7 in diameter and was supported in the borehole with the bottom thereof at a depth of about 1300 feet.

The leaching program on this well was initiated with the bottom of tubing 23 about 14 feet above the bottom of the hole. Fresh water was circulated in the normal direction, that is, through the tubing 23 and out through the annulus for about five minutes to clear the cuttings and to get the fresh water into the hole. Thereafter, salt water in reverse circulation was employed to backwash the hole. Such reverse circulation was of short duration, being terminated five to ten minutes after salt water first reached the surface through the tubing 23. Thereafter, normal circulation of fresh water continued for about ten to fifteen minutes. Reverse circulation of brine was then instituted to clean any insoluble material that had fallen down around the bottom of the tubing. The tubing and cavity were readily cleaned in this manner. When insoluble material ceased flowing out of the well through the tubing 23, reverse circulation was terminated and normal circulation of fresh water was again undertaken for a period of about ten to fifteen minutes longer than before, that is, for about one-half hour. The foregoing steps were repeated, increasing the normal circulation time for about ten to fifteen minutes until the cavity had a capacity of about 85,000 barrels. In those instances when the hole was not readily cleaned upon re verse circulation, the succeeding cycle of normal circulation was not increased in length but was of the same length as the preceding normal circulation cycle. Ditficulty in cleaning the hole during reverse circulation was taken as an indication of the presence of unusually large quantities of insoluble material whereupon it would be desirable to repeat the same leaching cycle on normal circulation rather than increase the length thereof.

In each case the reverse circulation was with brine water so that there was minimal leaching at the top of the hole.

When the capacity of the cavity reached about 85,000 barrels, one joint of pipe forming the tubing string 23 was then removed so that the bottom of the tubing was about 50 feet from the bottom of the hole.

Normal circulation with fresh Water was then initiated and continued until the well became plugged, that is, until there was experienced a 75 to pound p.s.i. pressure increase at the surface. Thereafter, the tubing 23 was raised and normal circulation established briefly to clear the tubing. Reverse circulation of brine was then initiated while lowering the tubing to the bottom of the borehole.

A fiow rate of'fresh water for leaching operations on the normal circulation cycle of about 425 to 500 barrels per hour resulted in an increase of capacity at the rate of about 1,000 barrels capacity per day.

By raising the washing orifice 23a at the bottom of the tubing 23 a substantial distance above the bottom of the cavity, leaching operations on normal circulation were continued for about 50,000 barrels. At the end of a fifty day period the tubing 23 began to plug as indicated by an increase in the tubing pressure. After cleaning out insoluble material as above described, the cavity had a capacity of about 140,000 barrels. The lower end of tubing 23 was again located about 40 feet above the bottom of the cleaned cavity and leaching operations were then resumed under normal circulation. During this step, about 65,000 barrels of formation were removed at a rate of about 1400 barrels per day before the Well again required cleaning. Thus, a substantial saving in time and effort was effected by utilizing normal circulation of fresh water with the washing orifice substantially above the bottom of the borehole and continuing such operation until a pressure increase indicated that the bottom of the well was full of debris.

Thus it will be seen that the present invention relates primarily to enlarging :a cavity in a soluble formation wherein a flow channel extends from the earths surface through an initial cavity to a point which is substantially less than the total depth of the cavity. A solvent is then introduced into the cavity through a tubing extending to such point and out through an annular flow path, carrying the formation material in solution. Such operation is continued until surface pressure on the first flow channel begins to increase. The bottom of the first flow channel is then elevated as to be well above the debris in the bottom of the hole and then lowered during reverse circulation until the debris in the bottom of the cavity is completely washed out through the tubing to the earths surface. This operation is completed when the tubing reaches bottom and efliuent liquid from the well ceases to carry insoluble material as detected in a storage pit. Thereafter, the tubing is raised from the bottom of the cavity and leaching operations are again resumed under normal circulation until a pressure rise again is noted on the input tubing.

Having described the invention and certain embodiments thereof, further modifications will now appear to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.

What is claimed is:

l. The method of enlarging a cavity in a salt formation in which substantial amounts of insoluble materials are embedded in a matrix of salt and having a first flow channel extending from the earths surface through said cavity to a point substantially above the bottom thereof and a second flow channel terminating in the region of the upper end of said cavity, which region of the upper end of said cavity is at a distance above the bottom of said cavity greater than said point, the steps comprising, introducing a salt solvent into said cavity through a washing orifice at the bottom of said first flow channel, discontinuing introducing said solvent into said cavity through said washing orifice when the pressure in said first flow channel begins to increase as a result of accumulation of insoluble materials at the bottom of said cavity near said washing orifice, thereafter elevating said washing orifice to a point a small distance above the surface of said insoluble materials and below said region of the upper end of said cavity, thereafter injecting a liquid in which said salt is substantially insoluble into said cavity through said second flow channel and withdrawing through said first flow channel, lowering said washing orifice simultaneously with said withdrawing, continuously and simultaneously entraining said insoluble materials by said injected liquid during lowering, completing lowering of said washing orifice substantially to the bottom of said cavity to remove said insoluble materials which produced said increase in said pressure, thereafter elevating said washing orifice substantially above the bottom of said cavity but to a point at a distance above the bottom of said cavity less than that of said region of the upper end of said cavcity, :and thereafter repeating the aforementioned steps until said cavity reaches the desired volume.

2. In a method of enlarging a cavity in a salt formation in which substantial amounts of insoluble materials are embedded in a matrix of salt and having a first flow channel extending from the earths surface through said cavity to a point substantially above the bottom thereof and a second flow channel terminating in the region of the upper end of said cavity, which region of the upper end of said cavity is at a distance above the bottom of said cavity greater than said point, said cavity enlarged by introducing a salt solvent into said cavity through a washing orifice at the bottom of said first flow channel and retracting the saturated solution for-med through said second flow channel; the improvement of the method for cleaning from said cavity bottom accumulated insoluble materials comprising the steps of: discontinuing introducing said solvent into said cavity through said washing orifice when the pressure in said first flow channel increases as a result of the accumulation of insoluble materials at the bottom of said cavity near said washing orifice, thereafter elevating said washing orifice to a point a small distance from the surface of said insoluble materials and below said region of the upper end of said cavity, thereafter injecting a liquid in which said salt is substantially insoluble into said cavity through said second fiow channel :and Withdrawing through said first flow channel, lowering said washing orifice simultaneously with said withdrawing, continuously and simultaneously entraining by said injected liquid said insoluble materials during lowering, and continuing lowering of said Washing orifice substantially to the bottom of said cavity to remove said insoluble materials which produced said increase in said pressure by the entraining action of said injected liquid downwardly around said first flow chan nel and into said washing orifice.

References Cited in the file of this patent UNITED STATES PATENTS 2,720,390 Brooks Oct. 11, 1955 2,745,647 Gilmore May 15, 1956 2,772,868 Brandt Dec. 4, 1956 2,787,455 Knapp'en Apr. 2, |1957 2,803,432 Teichmann et al Aug. 20, 1957 2,986,007 Shook May 30, 196 1 OTHER REFERENCES Oil and Gas Journal of Aug. 17, 1950, pages 59 and 60. 

1. THE METHOD OF ENLARGING A CAVITY IN A SALT FORMATION IN WHICH SUBSTANTIAL AMOUNTS OF INSOLUBLE MATERIALS ARE EMBEDDED IN A MATRIX OF SALT AND HAVING A FIRST FLOW CHANNEL EXTENDING FROM THE EARTH''S SURFACE THROUGH SAID CAVITY TO A POINT SUBSTANTIALLY ABOVE THE BOTTOM THEREOF AND A SECOND FLOW CHANNEL TERMINATING IN THE REGION OF THE UPPER END OF SAID CAVITY, WHICH REGION OF THE UPPER END OF SAID CAVITY IS AT A DISTANCE ABOVE THE BOTTOM OF SAID CAVITY GREATER THAN SAID POINT, THE STEPS COMPRISING INTRODUCING A SALT SOLVENT INTO SAID CAVITY THROUGH A WASHING ORIFICE AT THE BOTTOM OF SAID FIRST FLOW CHANNEL, DISCONTINUING INTRODUCING SAID SOLVENT INTO SAID CAVITY THROUGH SAID WASHING ORIFICE WHEN THE PRESSURE IN SAID FIRST FLOW CHANNEL BEGINS TO INCREASE AS A RESULT OF ACCUMULATION OF INSOLUBLE MATERIALS AT THE BOTTOM OF SAID CAVITY NEAR SAID WASHING ORIFICE, THEREAFTER ELEVATING SAID WASHING ORIFICE TO A POINT A SMALL DISTANCE ABOVE THE SURFACE OF SAID INSOLUBLE MATERIALS AND BELOW SAID REGION OF THE 